• The arm or leg electrode straps are too tight.
Actions
• Verify that the patient is comfortable, warm, and relaxed.
• Check all electrode contacts.
• If interference persists, turn the muscle-tremor filter on. If interference still persists, the
problem is probably electrical in nature. See the suggestions for reducing AC interference (in
a related troubleshooting tip).
AC interference
AC interference superimposes even-peaked, regular voltage on the waveforms.
Causes
• The patient or technician was touching an electrode during recording.
• The patient was touching a metal part of an exam table or bed.
• A lead wire, patient cable, or power cord are broken.
• Electrical devices in the immediate area, or lighting, or wiring concealed in walls or floors are
interfering.
• An electrical outlet is improperly grounded.
• The AC filter is turned off or set incorrectly.
Actions
• Verify that the patient is not touching any metal.
• Verify that the AC power cable is not touching the patient cable.
• Verify that the proper AC filter is selected.
• If interference persists, unplug the electrocardiograph from AC power and run it on the
battery. If this solves the problem, you’ll know that the noise was introduced through the
power line.
• If interference still persists, the noise may be caused by other equipment in the room or by
poorly grounded power lines. Try moving to another room.
Quick reference guide Troubleshooting
Lead alert or square wave
A dot might be flashing on the lead-status screen. Or one or more leads might appear as a square
wave.
Causes
• Electrode contact might be poor.
• A lead might be loose.
• A lead might be defective.